Three bolts and two cables detached the gas engine from the deck. Once removed I used a Tecumseh 90000A electric motor. This is a motor designed for lawnmowers - it's rated at 1.5HP continuous (using the "peak equals 3 times continuous" rule of thumb it should be good for about 4.5HP peak - and the gas motor being replaced was rated at 4HP). The 90000A also is designed to mount to a mower deck. The downside of the 90000A is the price - about $190 - however, I decided to go this route because it greatly increased my chances of success :-)

Two out of three holes on the 90000A lined up with my Sears Craftsman 22" deck. I simply drilled out the third. The old motor had threaded holes in the motor casing - the new one didn't have threading. So, three new nuts, bolts and washers to attach the motor.

I made the battery platform by simply cutting a piece of 2 by 4 and mounting it on the deck with angle brackets. This was one end of a support for a plywood battery deck. The other end simply rests on the rear end of the deck (I use a mulching blade so I'm not concerned about restricting the movement of the rear springloaded door). The batteries sit on top of this and are strapped down with two heavy duty rubber straps. This works for my environment - you might want something more sturdy depending on your yard layout.

The circuit is as follows:

The blade mounts to the keyed motor output shaft via a rectangular blade adapter. The output shaft itself is threaded - you slip on the adapter and then the blade and bolt both to the shaft. The old one was seized tight so I ordered a new one from Sears online parts store.

Notes:
1) I don't have a deadman's handle anymore. Both the breaker and the switch are in easy reach so I'm not concerned - however, an improvement would be to use the old springloaded handle with some form of high amp limit switch. I just re-read the above page and I notice that Lee is using the deadman's handle to operate the same style of breaker that I have - so I might try that out.
2) I placed the breaker between the batteries - it was a convenient place to mount it and I switch it off to allow both batteries to be charged seperately (with cheapo $18 1.5A battery chargers from Wal-Mart)
3) The volt meter was designed to mount into a 12V power socket (cigarette lighter) - so I just wired it to one of the two batteries - should be good enough.

The original mower was self-propelled and I didn't convert that feature. I might look at dismantling the engine casing and seeing if I can somehow salvage the gearing and output shaft for the self propel mechanism. But I probably won't bother. My yard isn't that big (we inherited the mower when we bought the house - I doubt I would have ever got a self propelled mower for our small yard).

Here's the parts list:

Part

Price in USD

Notes

Motor - Tecumseh 90000A

190

This used to be available as a surplus item for $70. Another approach would be to use a cheaper 1 to 1.5HP DC brushed motor with a shaft speed of about 3000 RPM - it should be relatively easy to create a mounting plate

50A Circuit Breaker, 50A Switch & #6 Gauge Lugs

25

Peak draw for this 24V system will be about 45A - in general you won't find this stuff in your local hardware store. Look at boat supply places instead

#6 Gauge wire

5

You can get this at Home Depot or Lowes

Assorted hardware

10

2 U1 sized flooded lead acid batteries

40

I'm hoping these cheapie batteries will have enough juice - I only mow my lawn about a dozen times a year (lots of tree cover) so if I get 50 cycles I'll be more than happy

Battery Platform

0

made from leftover scraps - I'm going for function here, not form!

Blade Adapter

8

You might not need this - my old one was seized on tight so I bought a replacement from www.sears.com

SUB TOTAL

278

Optional Accesories

Digital battery meter

15

2 cheapo 1.5A battery chargers

36

Sticking it to Condoleezza’s friends over at Chevron

PRICELESS

What more can I say? :-)

Yes, I can get a push mower for that price - and that's even more environmentally friendly. Yes, I can get a corded or low-end cordless mower for that price. However, a few counterpoints: (a) my deck is 22" - bigger than those options, (b) my batteries are removable and cheaply replacable, (c) I already had the mower so it's more eco-friendly to recycle than replace.

thanks chuck - but 1/2 as much as I think I can is twice as much as I want to do but only 1/4 of what I need to do. Or something like that anyway. ;-)

Yes, the batteries will be questionable - but at $20 each even if they don't do it I can always upgrade. (I don't even know what the Ah of these batteries are - I bought them because they were available and cheap (just like me :O ))

Arctic - is your B&D battery powered or corded? I am geeked at making my own (even though it was amazingly simple - I'm easily pleased!) - now of course there is still the question of whether it will cut the grass.

Thanks for the link and the tips!
You make it sound pretty easy and thanks to your sharing this it will be easier for the rest of us.
I have a nice little Honda self propelled but it's surely 15+ years old by now and probably spits out a lot more emissions than it used to. I know the muffler is going out on it finally.
This would be a fun little project and something I think I could (should) do.

Sounds like a good Winter project so it will be ready to use in the Spring.

That motor should work - but I'm not sure what type of winding it is - it has three inputs (whereas the simplest type of brushed motor just has two). If you over-volt it to 24V then you'll get double the RPM. I agree the $190 for the motor was steep - the guy whose design I copied got his as surplus stock for $70 I wasn't so lucky. The nice thing about the motor I used is that it's a drop in replacement with appropriate mounting points for mounting to the deck and mounting the blade and a simple two wire connection.

So, with your winch motor you'll need to figure out deck and blade mounting and you'll also have to determine the required connection for the three wires (assuming it's brushless then are there two windings to give two different speeds?)

Just a follow up ... I did buy that 12V motor - problem is it's an intermittent duty moter. Worked great for about 5 minutes and then I fried it. :( Now you know. I think it would work fine if you threw a load resistor in series with it that would take off maybe 2V - An $10 12" carbon rod perhaps (used for glass blowing)- though I'd expect it to get really hot.

Not sure what to do now, though ... there's a 24V version that's a higher HP that I think I could use continuous at 12V - that way I wouldn't have to redo my flange and shaft connection. I'll keep you posted.

I applaud your efforts with this mower. Reusing old equipment is the heart of recycling.

I am an eco-researcher and have stumbled across the CMM1200 cordless mower. I really like the mower and feel that it can be used on almost any yard now.

We should all do our part to save the enviroment and encourage the growth of the solar and wind power industries. Cordless electric lawn mowers go a long ways towards these goals. I recently purchased the Black & Decker Cordless Electric Lawnmower the CMM1200. I hope my review will help you make a decision about our future.